1. Field of the Invention
The present invention relates to a photovoltaic device to be applied to a solar cell assembly or a photosensor assembly, and more particularly to a photovoltaic device comprising a plurality of power generation regions comprising an amorphous semiconductor layer and the first and second electrodes formed on the top and bottom of the amorphous semiconductor layer, wherein the power generation regions are arranged in alignment with one another on an insulative substrate so that the power generation regions are electrically connected in series along the alignment. Still more particularly, the present invention relates to a method of producing the photovoltaic device.
2. Prior Art
FIG. 12 is a plan view of an example of a conventional photovoltaic device disclosed by Japanese Patent Publication No. 58-21827 (U.S. Pat. No. 4,281,208). FIG. 13 is a sectional view taken on line XIII--XIII in FIG. 12.
Referring to FIGS. 12 and 13, numeral 1 designates an insulative substrate. Numerals 2g-2i designate a plurality of first electrodes formed on the insulative substrate 1. Numeral 3 designates a continuous amorphous semiconductor layer coated on the first electrodes 2g-2i. Numerals 4b-4i designate a plurality of second electrodes coated on the amorphous semiconductor layer 3 and combined with the first electrodes 2g-2i respectively. The first electrodes 2g-i, the amorphous semiconductor layer 3 and the second electrodes 4g-4i are laminated to form and arrange power generation regions g-i in alignment with one another on the insulative substrate 1.
The insulative substrate 1 is made of transparent glass. The first electrodes 2g-2i are made of tin oxide, indium oxide or indium-tin oxide. The amorphous semiconductor layer 3 is made of, for example, an amorphous silicon layer having a P-I-N junction structure to generate electrons and/or holes by light illumination. The second electrodes 4g-4i are made of a metal such as nickel, aluminum, titanium or chromium. These component materials are common to those described in the following descriptions. The power generalion regions g-i are electrically connected as described below.
Numerals 21g-21i designate extended connection sections which are extended from the fringes of the first electrodes 2g-2i beyond the boundary of the amorphous semiconductor layer 3. Numerals 41g-41i designate extended connection sections which are extended from the fringes of the second electrodes 4g-4i beyond the boundary of the amorphous semiconductor layer 3. Among the extended connection sections 41g-41i of the second electrodes 4g-4i, the extended connection section 41h of the second electrode 4h in the power generation region h is laminated on the extended connection section 21g of the first electrode 2g in the power generation region g. The extended connection section 41i of the second electrode 4i in the power generation region i is laminated on the extended connection section 21h of the first electrode 2h in the power generation region h. The extended connection section 41g of the second electrode 4g in the power generation region g is connected to neither of the extended connection sections 21g-21i of the first electrodes 2g-i, but simply extended beyond the boundary of the amorphous semiconductor layer 3. A lead wire connection terminal 6i is formed on the extended connection section 21i of the first electrode 2i of the power generation region i. As a result, a photovoltaic device including the power generation regions g-i electrically connected in series is made. The electromotive force generated by this device is delivered across the extended connection section 41g of the second electrode 4g in the power generation region g and the lead wire connection terminal 6i formed on the extended connection section 21i of the first electrode 2i in the power generation region i.
Next, a method of producing the photovoltaic device having the structure described above is explained in the order of production process steps referring to FIGS. 14 (a)-(g).
FIG. 14 (a) shows a process step where the insulative substrate 1 is cleaned and dried (the first process step).
In FIG. 14 (b), a first electrode formation mask 22 having windows 22g-22i which in terms of shape and size correspond to the first electrodes 2g-2i and their extended connection sections 21g-21i of the power generation regions g-i is placed on the insulative electrode 1 (the second process step). In this masked condition, transparent conductive film is coated through the windows 22g-22i by a spraying, plasma CVD or sputtering method. When the mask 22 is removed, the first electrodes 2g-2i and their extended connection sections 21g-21i, which are arranged and formed on the substrate 1, are formed as shown in FIG. 14 (c) (the third process step).
As shown in FIG. 14 (d), the insulative substrate 1 is covered with an amorphous semiconductor layer formation mask 32 which has a continuous window 32a provided throughout the first electrodes 2g-2i and a cover section 32b covering all the extended connection sections 21g-21i. The shape and size of the mask 32 is equal to or nearly equal to that of the insulative substrate 1 (the fourth process step). When the masked substrate is placed in a plasma CVD unit, the amorphous semiconductor layer 3 is coated in the area corresponding to the window 32a by glow discharge decomposition. When the mask 32 is removed, the continuous amorphous semiconductor layer 3 is formed to cover the first electrodes 2g-2i as shown in FIG. 14 (e) (the fifth process step).
As shown in FIG. 14 (f), the amorphous semiconductor layer 3 is covered with a second electrode formation mask 42 having windows 42g-42i which in terms of shape and size correspond to the second electrodes 4g -4i and their extended connection sections 41g-41i in the power generation regions g-i and also has a window 42i' which in terms of shape and size corresponds to the lead wire connection terminal 6i (the sixth process step).
In this masked condition, metal film is coated through the windows 42g-42i and 42i' by sputtering, resistance heating or electronic beam method. When the mask 42 is removed, the second electrodes 4g-4i, their extended connection sections 41g-41i and the lead wire connection terminal 6i are formed on the amorphous semiconductor layer 3 as shown in FIG. (g) (the seventh process step).
In the case of the conventional photovoltaic device described above, the connection area (including the connection sections) of the power generation regions g-i is formed like a belt beyond the boundary of the power generation regions as indicated by letter C in FIG. 12. This belt-shaped connection area C occupies 15-20% of the total plane area of the insulative substrate 1. Therefore, the area coated with the amorphous semiconductor layer 3, that is, the ratio of the effective light-receiving area (indicated by letter G in FIG. 12) to the connection area is reduced. Accordingly, when this photovoltaic device is applied to power supply units of pocket calculators and clocks, the size of the insulative substrate 1 becomes large in order to deliver current required for such units. In other words, the output-to-size ratio is small and thus units incorporating such a photovoltaic device are apt to become large. In addition, the connection area C which is useless in photovoltaic effect needs to be covered and puts restrictions on the internal layout,of units.
Furthermore, in the case where the conventional photovoltaic device is produced by the above-mentioned process, the mask 32 is used to prevent the amorphous semiconductor layer 3 from entering the connection area C when the amorphous semiconductor layer 3 is coated, as described in the fourth process step. However, it is inevitable that a part of the amorphous semiconductor layer 3 enters the gap between the mask 32 and the insulative substrate 1. Therefore, it is necessary to increase the reliability of the connection between the extended connection sections 21g-21i of the first electrodes 2g-2i and the extended connection sections 41g 41i of the second electrodes 4g-4i. For this purpose, the laminated areas of these extended connection sections need to be made larger. This causes the above-mentioned output-to-size ratio to reduce further. Moreover, due to use of the mask 32, plasma interference is caused by glow discharge when the amorphous semiconductor layer 3 is coated. In particular, interference fringes remain on the amorphous semiconductor layer 3 at the window edges of the mask. As a result, film quality is deteriorated, the output of the photovoltaic device drops and the appearance of application units becomes deteriorated. Moreover, as the mask 32 is subject to repeated use, the mask is deformed. As a result, the positioning accuracy of the mask reduces and the production yield of the photovoltaic devices greatly reduces due to dislocation of the mask.
In the above-mentioned conventional photovoltaic device, the amorphous semiconductor layer 3 is a continuous type provided throughout the power generation regions g-i. In addition to this continuous type, the amorphous semiconductor layer 3 can be a segmented type. This segmented type is made as described below. After a continuous amorphous semiconductor layer is coated and formed throughout a plurality of power generation regions, grooves are formed by irradiation of a laser beam to separate the layer at the boundaries of all the power generation regions and to connect the first electrode of a power generation region to the second electrode of the adjacent power generation region so that separated regions are electrically connected one another.
Segmented types which have been known are disclosed in U.S. Pat. Nos. 4,292,092, 4,542,578, 4,315,096, 4,518,815 and 4,645,866. Among these, U.S. Pat. No. 4,645,866 relates to a prior application by the same assignee as that of the present invention. As a typical example of such a segmented type, the structure and the production method for the photovoltaic device of the prior application are briefly explained referring to FIGS. 15, 16 and 17 (a)-(e).
As shown in FIG. 17 (a), the first electrodes 2g-i are coated and formed on the insulative substrate 1. On the first electrodes 2g-i, the continuous amorphous semiconductor layer 3 is coated throughout all the power generation regions g-i as shown in FIG. 17 (b). Next, the second electrodes 4g-4i are coated and formed as a continuous layer on the entire surface of the amorphous semiconductor layer 3 as shown in FIG. 17 (c). By irradiation of a laser beam, the second electrode layers and the amorphous semiconductor layer 3 are removed at the positions where the first electrodes 2g-2i are adjacent to one another and grooves 7g-7i are provided to form the independent power generation regions g-i as shown in FIG. 17 (d). Conductive metal paste is filled in the grooves 7g-7i by printing or other methods as shown in FIG. 17 (e) and is, fired to form conductive connection sections 8g-8i so that the power generation regions g-i are electrically connected. As the final step, the second electrodes 4g-4i and the amorphous semiconductor layer 3 are removed by irradiation of a laser beam to form grooves 9g-9i and to expose the first electrodes 2g-2i. As a result, the power generation regions g-i are connected in series. By following these steps, the photovoltaic device having the structure shown in FIGS. 15 and 16 are produced.
Although the segmented type described above slightly differs from other segmented types in its production process, they are common in that grooves are formed perpendicular to the arrangement direction of a plurality of power generation regions to divide and electrically connect the power generation regions. The connection section of each power generation region of the conventional segmented type photovoltaic device described above can have an area smaller than that of the continuous type photovoltaic device described in the beginning of this specification. Thus the effective light-receiving area of an insulative substrate having a predetermined size can be increased. Due to this structure, the segmented type is advantageous to increase the output-to-size ratio of a power generation device used in application units such as pocket calculators and clocks. In addition, no mask is necessary when the amorphous semiconductor layer is coated. This does not cause problems such as deterioration of film quality, reduction of output due to deterioration and reduction of production yield due to mask deformation caused by repeated use of the mask.
However, in all the above-mentioned conventional segmented type photovoltaic devices, when the number of power generation regions is N, N-1 grooves must be provided by cutting. Conductive metal paste must be filled in the grooves . In this way, considerably large connection sections must be formed and special material must be used at the connection sections. In the case of U.S. Pat. No. 4,645,866 for example, N-1 grooves are additionally necessary to connect the power generation regions in series. Therefore, the number of cutting steps increases and productivity is limited. In addition, special considerations are necessary to ensure the reliability of electrical connection between the conductive metal paste (connection material different from the first and second electrodes) and the first and second electrodes. This also adversely affects productivity.